1. Field of the Invention
The present invention relates to a linear motor drive apparatus, and more particularly, to a linear motor drive apparatus suitable for application between a fixed element and a movable element of a precision machine tool.
2. Related Art
Research has been done with regard to a linear motor drive apparatus, to replace a drive apparatus formed by a combination of a ball screw and a nut, for the purpose of straight-linearly feeding a movable element, such as a work table or spindle stand, relative to a fixed element, such as a machine frame, of a precision machine tool. This linear motor has a row of magnets arranged on the fixed element, and a row of magnets arranged on the movable element.
Because the movable element of such a linear motor drive apparatus is guided by a guide mechanism provided in the fixed element, it is allowed to move along a reference plane for design of the guide mechanism, for example, a center plane thereof that divides the guide mechanism into two equal parts, left and right.
For this reason, a linear motor drive apparatus can be envisioned in which the magnets are arranged in parallel at both sides of the above-noted reference plane.
One target of research is determining how to arrange the magnets.
Another target of research is determining how to reduce a tendency toward cogging of the movable element of the linear motor drive apparatus (a jerking movement thereof, occurring when moving in a straight line) and yawing of the movable element (a rocking thereof from left to right).
Another target of research is developing a guide mechanism that achieves stable movement of the movable element.
There is a method of shifting the arrangement positions of the magnets by one-half pitch to the left and the right, so as to reduce the cogging of the movable element. Reducing the cogging using this method, however, results in an increase in yawing.
Accordingly, it is an object of the present invention to provide a linear motor drive apparatus, which reduces the cogging without an increase in the yawing.
In order to achieve the above-noted object, the inventors of the present invention discovered that, with planar symmetry between parallel rows of magnets and the reference plane, by providing a steel sheet parallel to the reference plane at an intersection between the movable element and the reference plane, if the shape of the steel plate is made narrow at the end, and in particular if it is made triangular, cogging of the movable element is reduced, that if the steel plate is provided symmetrically with respect to both sides of the movable element in the direction of movement of the movable element, there is a further prominent reduction in cogging, and that these effects are achieved regardless of whether the row of magnets mounted to the fixed element is a row of electromagnets or a row of permanent magnets.
Given the above, a first aspect of the present invention is a linear motor drive apparatus having a fixed element, which has a guide mechanism, a movable element, which is guided by the guide mechanism and which can move along a prescribed reference plane, a row of first magnets, which is mounted to the fixed element, and which is disposed in parallel to both sides of the reference plane, and a row of second magnets, which is mounted to the movable element, and which is disposed in parallel to both sides of the reference plane, wherein there is planar symmetry of the first parallel row of magnets with respect to the reference plane, and wherein a steel plate is provided in parallel with the reference plane, the steel plate having a narrowed end part.
According to this aspect of the present invention, by providing a steel plate in parallel to the reference plane at the intersection with the reference plane of the movable element, and narrowing an end part of the steel plate, cogging of the movable element is reduced, as can be understood from the discoveries of the inventors. Furthermore, because the row of first magnets is made to have planar symmetry with respect to the reference plane, yawing is also reduced.
A second aspect of the present invention is a variation on the linear motor drive apparatus of the first aspect, wherein the steel plate has a triangular shape. According to this aspect of the present invention, as is clear from the discoveries of the inventors of the present invention, there is a prominent reduction in cogging of the movable element.
A third aspect of the present invention is a variation on the linear motor drive apparatus of the first aspect, wherein the steel plate is provided so as to have planar symmetry with respect to both ends of the movable element along the direction of movement thereof. According to this aspect of the present invention, as is clear from the discoveries of the inventors of the present invention, there is a further reduction in cogging of the movable element, A fourth aspect of the present invention is a variation on a linear motor drive apparatus of any one of the first to the third aspects, wherein the row of first magnets comprises electromagnets, and wherein the row of second magnets comprises permanent magnets. According to this aspect of the present invention, as is clear from the discoveries of the inventors of the present invention, cogging of the movable element is reduced.
A fifth aspect of the present invention is a variation on a linear motor drive apparatus of any one of the first to the third aspects, wherein the row of first magnets comprises permanent magnets, and wherein the row of second magnets comprises electromagnets. According to this aspect of the present invention, as is clear from the discoveries of the inventors of the present invention, cogging of the movable element is reduced.
A sixth aspect of the present invention is a variation on a linear motor drive apparatus of any one of the first to the fifth aspects, wherein the guide mechanism is a pair of V-shaped grooves that have planar symmetry with respect to the reference plane. According to this aspect of the present invention, the movable element moves in a stable manner.